(a) Field of the Invention
The invention relates to image processing system, particularly to video source system and television system.
(b) Description of the Related Art
Since the entering of the 20th century, the development of television technology and its applications has proven that it is now part of human life and core of entertainment. Because of the improvement of display technology in recent years, providing massive data and high-definition images has become the focus of the future development of the television industry. Please refer to FIG. 1, showing a schematic diagram of a typical television system and its video source. As shown in FIG. 1, the video source system 110 transmits video data in analog signal format to a television system 120 for broadcasting video pictures. Although a digitized transmission interface has already become available, an analog transmission interface is still most commonly used.
The video source of the television system 120 can take many forms, such as a DVD player, set top box, and even various game consoles. In general, the components of the video source system 110 comprise a video encoder 112 for performing image data encoding, and a digital-to-analog converter (DAC) 114, which converts the encoded digital signal into an image analog signal and outputs the image analog signal.
The television system 120, such as a LCD TV or other flat panel television system or digital television system, which is becoming the main stream applications, receives an image analog signal transmitted from the video source, converts it into digital format with an analog-to-digital converter (ADC) 124, and performs decoding operation with a video decoder 122 for further image processing and broadcasting.
There are many types of video encoding format. The most commonly available ones are: CVBS signal format, luminance chrominance (YC) signal format, and color difference (YPrPb) signal format and so forth. Therefore, the analog transmission interface for transmitting video signals between the video source system 110 and the television system 120 can also be one of several types, such as AV interface for transmitting signals in the CVBS format; S-video interface for transmitting signals in the YC format; and color difference video interface for transmitting signals in the YPrPb format. Among the above-mentioned various signal formats, the CVBS signal, the Y signal of the S-video, and the Y signal of the color difference video, all comprise not only the components corresponding to image data but also the synchronizing signal component for performing synchronization operation.
FIG. 2 shows a schematic diagram illustrating an analog video signal comprising both the image data and the synchronizing signal. As shown in FIG. 2, in the case of the CVBS signal format, the video signal comprises the image signal CVBS and the synchronizing signal (Sync signal) S. The typical signal level range of the image signal CVBS covers 0˜0.7V while that of the synchronizing signal S covers −0.3V˜0V. The image signal CVBS comprises the image data that will be actually displayed to the users, while the synchronizing signal S comprises the prerequisite information for performing synchronizing operation. Although the synchronizing signal S is not displayed, it is still transmitted to the later stage receiving circuit as the reference basis for synchronization operation. Therefore, the dynamic ranges of the digital-to-analog converter 114 and the analog-to-digital converter 124 have to cover both the ranges of the image signal CVBS and of the synchronizing signal S, which result in a total dynamic range of 1V.
In general, for the television system, certain requirements on the resolution of the image signal component contained in the analog video signals transmitted are necessary to assure the picture quality while broadcasting. Thus, the digital-to-analog converter 114 and the analog-to-digital converter 124 both have to support up to certain number of significant bits. However, due to factors_such as capacitance and impedance matching during semiconductor manufacturing process, the more the number of significant bits of the digital-to-analog converter 114 and the analog-to-digital converter 124 is, the more the manufacturing cost and the design complexity becomes. This situation becomes more aggrieved when considering the fact that the synchronizing signal occupies part of the dynamic range, because in order to achieve the same resolution, it requires even more significant bits to cover a larger dynamic range.